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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #391
    Noob Stycker's Avatar
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    Re: Ask an Acoustic Engineer (me)

    You guys are a wealth of knowledge. I didn't even know that headroom req. was displayed there in the EQ section. Hopefully that means it never popped up so I never saw it. I will be looking from now on. Thank you.

  2. Back To Top    #392
    Noob Jdunk54nl's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Stycker View Post
    You guys are a wealth of knowledge. I didn't even know that headroom req. was displayed there in the EQ section. Hopefully that means it never popped up so I never saw it. I will be looking from now on. Thank you.
    Most dsp's shows something similar too. But, this doesn't mean you can't go over 0db on these, it all depends on where do you get 0dbfs. Like I just had an issue with my mids. I may have boosted an area by 12db (trying to make it louder overall instead of boosting 6db and cutting the rest by 6db), this was too much and when I turned the volume up near max, issues were heard and I instantly turned it back down. I wasn't sure if I was going to be able to get away with it or not, so I was careful with the volume and turned it up slowly. It was literally at volume 38 out of 39 max that a problem came about. If it wasn't for an issue like that, I would have left the boost and went on my way. If I was using a adau eval board, I could have gotten around this issue in more creative ways with frequency dependent limiters.

    Like helix shows it with anything over the 0 line
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    and similar for dayton

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    and jl
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    and minidsp (this was for my outdoor speakers....may have boosted a bit, set a very steep 48db crossover after, and used the limiters on the minidsp so we can't break the system even at max volume). I wish it was frequency limiters, but I haven't purchased a adau chip eval board for this stuff yet.

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    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  3. Back To Top    #393
    Noob Jdunk54nl's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Also, on the home side of things, Dirac live will cut the overall volume by 10db. This gives it 10db of headroom overall to boost. So if you set a channel gain to say -6db, and boost somethign by 6db, on the graph it will show you went over 0db by 6db. But in reality you are at 0db because you cut everything by 6db. And this would only be true if you were actually driving EVERYTHING to its max output. So the number to the left (currently says 0db) needs to actually read 0db output when you have everything maxed out (and something is actually playing) for all of this to be true.

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    So the TL/DR version of all of this. Boosting and cutting is much much more complicated than what people make it out to be whether or not its safe to do. This is probably why the general consensus gets to just cut and no boost. You will definitely be safer with that approach, but will loose overall volume.
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  4. Back To Top    #394
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    Re: Ask an Acoustic Engineer (me)

    I clipped my midbass once by over boosting. Everything was fine until I did a Global EQ with the Virtual channels. I have a drop out at 60 hz. I boosted 60 hz in both regular output and virtual output. Be very careful boosting in Virtual channels.

  5. Back To Top    #395

    Re: Ask an Acoustic Engineer (me)



    What's going on when the cone appears to wobble like ^^^that^^^ in videos of subwoofer excursion.


    I've always assumed it's at least in part an optical illusion, as I assume there's not enough gap width to allow the coil the amount of non-linear lateral movement that such a wobble would seem to imply.
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  6. Back To Top    #396
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    Re: Ask an Acoustic Engineer (me)

    If these help with the question Grinder posted (my sub), they're the scope readings at different freq's. I highpassed on the amp at ~15hz and the sub is running @1ohm.
    Measurements taken during gain-setting with the HU volume set at 30/35. Normal listening is 15-20/35.
    No DSP but the sub is lowpassed on the HU at 100hz/-24db slope
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  7. Back To Top    #397
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Grinder View Post
    What's going on when the cone appears to wobble like ^^^that^^^ in videos of subwoofer excursion.

    I've always assumed it's at least in part an optical illusion, as I assume there's not enough gap width to allow the coil the amount of non-linear lateral movement that such a wobble would seem to imply.
    Wow that seems like a crazy rocking mode. I've been thinking about this a couple days and don't have a really strong answer.

    My best guess is yes, there is some amount of optical illusion because the surround seems (?) to rock sideways more than the cone does. Pay attention to the tilt of the dust cap relative to the tilt of the surround. This might be true, but it's hard to tell without slowing it down and examining in greater detail. You could get a strobe light to explore more. Parts Express has a new one that's reasonably priced. If the frequency is pretty low like 30hz 'ish, then you can get a strobe light app for your phone. The phone apps seem to struggle with strobe frequencies above 40hz'ish ... or at least my phone does.

    You're also right that the amount of clearance in the magnetic gap is usually pretty tight and would not allow this kind of wild rocking mode behavior. Seems a bit exaggerated for sure.

    A pretty sharp coworker once said he likes to build ported boxes with symmetric dimensions and port placement, otherwise he would see rocking modes like this from the uneven air pressures in the box if you place the ports along the bottom edge only.

    I don't have a strong answer for this one, hard to tell what's going on from this side of the internet!
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
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  8. Back To Top    #398

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    Wow that seems like a crazy rocking mode. I've been thinking about this a couple days and don't have a really strong answer.

    My best guess is yes, there is some amount of optical illusion because the surround seems (?) to rock sideways more than the cone does. Pay attention to the tilt of the dust cap relative to the tilt of the surround. This might be true, but it's hard to tell without slowing it down and examining in greater detail. You could get a strobe light to explore more. Parts Express has a new one that's reasonably priced. If the frequency is pretty low like 30hz 'ish, then you can get a strobe light app for your phone. The phone apps seem to struggle with strobe frequencies above 40hz'ish ... or at least my phone does.

    You're also right that the amount of clearance in the magnetic gap is usually pretty tight and would not allow this kind of wild rocking mode behavior. Seems a bit exaggerated for sure.

    A pretty sharp coworker once said he likes to build ported boxes with symmetric dimensions and port placement, otherwise he would see rocking modes like this from the uneven air pressures in the box if you place the ports along the bottom edge only.

    I don't have a strong answer for this one, hard to tell what's going on from this side of the internet!
    Thank you. I hadn't noticed it before, but now that you mention it, I see what you mean about the dust cap moving more linearly than the surround. That's a really cool idea to use a strobe light to see what's really going on.
    "That's all, folks!"

  9. Back To Top    #399
    Owner BigAl205's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Video cameras scan left to right, top to bottom. At certain frequencies, it just looks distorted.

  10. Back To Top    #400
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by BigAl205 View Post
    Video cameras scan left to right, top to bottom. At certain frequencies, it just looks distorted.
    Solid! This would make so much more sense.

    A strobe light could tell you for sure, but that's hard to video record too.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
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